Structural investigations of nanomixed oxides SnO2–xAl2O3 prepared by sol–gel technique

Nanosize polycrystalline sample of the mixed oxides SnO2 + xAl2O3 (x = 0, 25, 50, 75 wt%) were synthesized by sol–gel technique. The resulting samples were characterized with X-ray powder diffraction (XRD), differential thermal analysis (DTA) and thermogravimetric analysis (TGA). Rietveld quantitative phase analysis shows that part of alumina is incorporated into the SnO2 lattice while the other part remains as a separate phase. For the incorporated part, some Al3+ are accommodated substitutionally for Sn3+ and some is segregated on the grain boundary surface of SnO2. It is found that the grain size of the mixed oxides SnO2 + xAl2O3 is below 10 nm while for pure SnO2 it is over 41 nm, indicating that alumina can effectively prevent SnO2 from further growing up in the process of calcination. This is confirmed by the big increase in the specific surface area for mixed oxide samples.

Research highlightsThis work reports about the effects of alumina on the structural and microstructural properties of stannic oxide prepared by sol–gel technique. Alumina is found to play the role of a surfactant in preventing the nanoSnO2 particles from agglomeration into large particles, resulting in high specific surface area needed in many fields of applications. Part of alumina is deposited on the SnO2 grain surface as a highly dispersed amorphous oxide coating on the SnO2 nanocrystallites.